Engine lubricant compositions may be selected to provide increased engine protection, as well as an increase in fuel economy, and a reduction in emissions. However, in order to achieve benefits of improved fuel economy and reduced emissions, a balance between engine protection and lubricating properties is required for the lubricant composition. For example, an increase in the amount of friction modifiers may be beneficial for fuel economy purposes but may lead to reduced ability of the lubricant composition to handle water. Likewise, an increase in the amount of anti-wear agent in the lubricant may provide improved engine protection against wear but may be detrimental to catalyst performance for reducing emissions.
The same is true for the soot and sludge handling components of a lubricant composition. Dispersants are added to lubricant compositions to keep the soot and sludge in suspension and prevent the contaminants from settling on and/or adhering to surfaces. As the amount of dispersant(s) in a lubricant composition is increased, typically, the soot and sludge handling properties of the lubricant are improved. For use with heavy duty diesel engines, the treat rates for a dispersant to be effective are very high. However, high dispersant treat rates increase corrosion and are harmful to seals. Accordingly, there is a need for dispersants, or a dispersant combination that can provide satisfactory soot handling properties to the lubricant composition using a relatively lower treat rate of the dispersant. Such lubricant compositions should be suitable for meeting or exceeding currently proposed and future lubricant performance standards.